The present invention relates to a method and apparatus for finish rolling workpieces of substantially circular cross-section to a selected diameter.
The possibility of finish rolling workpieces to a selected diameter have already been described in a thesis of Peter Kron (Technical College Braunschweig) with the title "The Finish Rolling of Cylindrical Workpieces by Rolls Movable Toward Each Other". On page 94 of this thesis in paragraph 8.2.1 three possibilities of finish rolling of a workpiece to a selected diameter and the preconditions therefor are mentioned, and the obtainable results described. The best results are obtained during finish rolling with an indicating control (FIG. 44). The indicating control relates to the control of the rolling force P.sub.w. If the force P.sub.w reaches a predetermined size, the rolling process is finished.
This method has the disadvantage that desired results can be repeated only with varying rolling times. Therefore, this method is unsuitable for mass production, due to the varying rolling time per workpiece. Furthermore, with this method it is not possible to obtain during changing operating conditions a constant workpiece tolerance, since the spatial position of the apparatus elements and the elastic behavior of the latter change during changing of the temperature, which will entail a corresponding change in the workpiece tolerance. It is also not possible by increasing the rolling time to reach, for the workpieces of a series always the same force P.sub.w required by Kron. Depending on the material structure of a workpiece and the starting tolerance, it is not possible, even by increasing the rolling time, to obtain always the same force P.sub.w required by Kron.
According to another, in the aforementioned thesis described rolling method, the working rolls are moved towards each other until a predetermined desired value is reached. The reaching of this desired value is thereby determined by contact of the working rolls, respectively of elements connected thereto, with adjustable stops.
The adjustment, respectively the determination of such a desired value causes considerable difficulties since the bending of the rolls, the bearing trunions thereof, compression of bearing parts, as well as distorsion of the roll stand, etc. add up to an error in the position of the roll surfaces in the working region which can be hardly calculated. Since a direct measurement at the contact points between working rolls and workpiece is not possible, this measurement has to be carried out at the edge of the peripheral surface of the rolls, or in the region of the bearing trunions thereof, so that deviations from the desired value cannot be ascertained.